1. Field of the Invention
The present invention relates to an apparatus for generating a sync of a digital television, and more particularly, to an apparatus for generating a sync of a digital television which provides a stabilized synchronization to an analog signal inputted thereto so as to be processed regardless of a standard system or a nonstandard system.
2. Description of the Background Art
Currently, digital television and analog television coexist. Accordingly, digital televisions format-converts an analog image signal of an NTSC (national television systems committee) through a digital signal processing for displaying it as well as displaying a 18-format digital image stream of an ATSC (advances television systems committee).
When the NTSC analog image signal is format-converted to a high definition (HD) to be displayed, a clock and sync signal related to display is determined by the number of frames included in a digital image stream in the ATSC system and a picture resolution. And in case that the NTSC analog image and VGA signal are displayed on the same resolution their clock and sync signal generation structures related to display are to be the same each other.
The ATSC system includes two standardized display mode of 59.9 Hz and 60 nz Thus its display clock accordingly has a selective clock For example, in case that it""s a display mode of an interlaced scanning method having a screen resolution of 1920xc3x971080, a horizontal sync is 2200 clock and a vertical sync is 562 5 line, its display clock has 74.175 MHz and 74.25 MHz for the 55.94 Hz and 60 Hz, respectively.
However, the digital television originally designed to process the standardized sync signal such as the ATSC digital image stream in accordance with the conventional art as described above has the follow leveling problems when it processes nonstadardized signals such as the NTSC analog image signal.
First, when the digital television (DTV) is designed to process both a digital data and an analog signal, the ATSC system and the NTSC system are independently designed. In this case, it is difficult to implement a unified user interface in a single system for the two sources of the ATSC and the NTSC. Also, an additional function such as a PIP (picture in picture) is hardly implemented.
Secondly, in order to implement a unified user interface (UI) regardless of an analog or a digital input signal in a system, a stable display sync should be provided for whatever case that an ATSC-converted signal is inputted or that an NTSC-converted signal is inputted. For this purpose, for the NTSC analog image signal, a nonstandard signal can be stabilized by a time base correction (TBC) processing. In this case, however, field skip or repeat occurs periodically for the standard signal before or after the TBC processing, which causes variation in a frame ratio and thus, a time display error is generated in a motion picture.
Nevertheless, if an output sync is unconditionally locked with an input sync, since the unstable input sync in the nonstandard case is transmitted to the output screen as it is, the unstable display synchronization affects a deflection unit, inevitably causing a screen instability and OSD flickering
Thirdly, in case where the processing method for a standard signal and a nonstandard signal is divided by a lock and unlock method, the follow leveling problems arise. That is, when a general broadcasting signal, that is, a standard signal, is instantly weakened and is erroneously recognized as a nonstandard signal and then returns to its normal state to be re-recognized as a standard signal, there is a sync instability according to the signal transition period. In addition, a sync signal is unstable due to a forcible conversion such as a function of normal play a pause function for suspending a picture of a screen and two-time speeding in a VCR.
Therefore, an object of the present invention is to provide an apparatus for generating a sync signal of a digital television ensuring a stable synchronization for processing an analog signal regardless of whether an external input signal (i.e., an analog signal) inputted to a digital television is a standard signal or a nonstandard signal.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for generating a sync signal of a digital television in which an analog component data inputted from a component data (YcbCr) write controller is converted to a digital data and the converted digital data is stored in a frame buffer including a vertical sync phase controlling unit for varying a clock frequency of a voltage control crystal oscillator according to a phase difference between an input vertical sync signal (Vsync_in) and a vertical sync signal (Vsync) generated in a final output terminal, to reduce the phase difference; a component data read controlling unit for dividing the clock frequency, outputting a read control signal to read the signal stored in the frame buffer in synchronization with the clock frequency, and outputting a horizontal and a vertical syncs (Hsync)(Vsync); a frequency converter for converting the output frequency to generate a display clock; a format converter for converting the digital signal as read from the frame buffer according to the horizontal and the vertical syncs (Hsync)(Vsync) outputted from the component data read controlling unit to a display format and outputting the format-converted signal for display according to a display clock outputted from the frequency converter
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.